Amos jokes that his secret relationship with Mary may work in his favour, while Brand adopts a unique method of sitting on her butter to melt it before baking.
Watch the Comic Relief Bake Off teaser:
Amos and Brand are among the list of celebs tackling the baking reality show, which also includes Andy Akinwolere, Duncan Bannatyne, Julia Bradbury, Ed Byrne, Warwick Davis, Helen Glover, Martha Kearney, Bob Mortimer, Ingrid Oliver, Simon Reeve, Ellie Simmonds, Kirsty Wark, Lorna Watson and Claudia Winkleman.
At the end of every episode, one celebrity will be crowned the Star Baker. The show's purpose is to inspire the nation to host their own bake sales and raise money for Comic Relief.
The Great Comic Relief Bake Off book will be sold in Sainsbury's, while an Emma Bridgewater apron as worn by The Great British Comic Relief Bake Off stars is being sold in TK Maxx and Homesense, raising money for the charity.
Bake Off celeb Claudia Winkleman said: "I am actually obsessed with baking. I often cover the kitchen in flour and I have three whisks. I have only ever made two things - a Victoria sponge and chocolate cookies.
"It turns out the Bake Off is about other things too. I had the most brilliant time and have baked more since taking part. But I refuse to try pastry, I can't even discuss it."
The Great Comic Relief Bake Off airs from Monday, January 21 to Thursday, January 24 on BBC Two.